Method of fabricating semiconductor device

ABSTRACT

A method of fabricating a semiconductor device according to the invention comprises forming a capacitor comprising a lower electrode formed on a semiconductor substrate, a capacitive insulator made up of a metal oxide film, formed on the lower electrode, and an upper electrode formed on the capacitive insulator; forming a metal pattern to be electrically connected to the electrodes of the capacitor; forming a first protection film which coats at least a side face of the metal pattern; and forming a water constituents diffusion preventive film on the side face and top face of the metal pattern through the intermediary of the first protection film. As a result, a method of fabricating a ferroelectric memory capable of protecting a ferroelectric capacitor from water constituents evolved during a fabrication process, and maintaining satisfactory memory characteristics can be provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device and amethod of fabricating the same, and in particular, to a semiconductordevice comprising a ferroelectric memory employing a highlyferroelectric film as a capacitive insulator and a method of fabricatingthe same.

[0003] 2. Description of the Related Art

[0004] In recent years, attention has been focused on a semiconductormemory called a FeRAM (Ferroelectric Random Access Memory) comprising acapacitor that employs a ferroelectric film for a capacitive insulator,as the coming generation of a nonvolatile memory.

[0005] With a conventional ferroelectric memory, a ferroelectriccapacitor comprising a capacitive insulator made up of a ferroelectricfilm, and an upper electrode and a lower electrode with the capacitiveinsulator interposed between the electrodes is formed on a semiconductorsubstrate with an integrated circuit comprising transistors and sofroth, formed thereon.

[0006] Further, a silicon oxide film serving as an interlayer insulatoris formed on top of the semiconductor substrate and the ferroelectriccapacitor, and after removal of water constituents contained in theinterlayer insulator by heat treatment, contact holes reaching theintegrated circuit or the ferroelectric capacitor, provided on thesemiconductor substrate, are formed in the interlayer insulator.

[0007] A metal pattern made of material such as aluminum (Al), titanium(Ti), or tungsten (W), and so forth is formed inside these contactholes, and is electrically connected to the integrated circuit and theferroelectric capacitor, respectively. Further, a passivation filmserving as a protection film is formed on the respective metal patterns.

[0008] With a capacitor making up a conventional FeRAM, an insulatingfilm made of a metal oxide such as strontium bismuth tantalate(SrBi₂Ta₂O₉) called as SBT, lead zirconate titanate (Pb(Zr, Ti)O₃)called as PZT, and so forth is used for a capacitive insulator made upof a ferroelectric film.

[0009] Further, a noble metal is generally used as the constituentmaterial of the upper electrode and lower electrode. This is because atthe time of forming a highly ferroelectric film, and at the time ofimproving the film quality of the capacitive insulator after theformation of the capacitor, the electrodes making up the capacitor cometo be exposed to a high temperature oxidizing atmosphere, so thatoxidation resistance is highly required of the constituent material ofthe electrodes. Particularly, in the case of the conventionalferroelectric capacitor, platinum (Pt) is used as a constituent materialof the electrodes from the viewpoint of cost, process stability, ease inthe fabrication of the ferroelectric film, and excellent workability.

SUMMARY OF THE INVENTION

[0010] In developing the present invention relating to a semiconductordevice comprising a ferroelectric capacitor, particularly using a noblemetal having a catalytic action as a constituent material of electrodes,attention has been focused on hydrogen molecules evolved due tooxidation of the surface of metal patterns made of Al, Ti, W, or soforth in the course of water constituents such as constitution water,contained in a silicon oxide film making up interlayer insulators,adsorption water evolved in a cleaning process, and so forth undergoingthermal diffusion following heat treatment applied in later stages.

[0011] It is therefore an object of the invention to provide a method offabricating a semiconductor device comprising a ferroelectric memorymaintaining satisfactory memory characteristics by decreasing evolutionof the hydrogen molecules, and suppressing evolution of hydrogen atomsthat cause metal oxides of a ferroelectric film, produced by the agencyof the catalytic action of the constituent material of the electrodes,to undergo reduction. Further, it is another object of the invention toprovide a method of fabricating a semiconductor device capable ofprotecting a ferroelectric capacitor from water constituents evolved infabrication steps after the formation of the ferroelectric capacitor.

[0012] In accordance with a first aspect of the invention, there isprovided a method of fabricating a semiconductor device comprising:

[0013] a step of forming a capacitor comprising a lower electrode formedon a semiconductor substrate, a capacitive insulator made up of a metaloxide film, formed on the lower electrode, and an upper electrode formedon the capacitive insulator;

[0014] a step of forming a metal pattern to be electrically connected tothe electrodes of the capacitor;

[0015] a step of forming a first protection film for coating at least aside face of the metal pattern; and

[0016] a step of forming a water constituents diffusion preventive filmon the side face and top face of the metal pattern through theintermediary of the first protection film.

[0017] Further, in accordance with a second aspect of the invention,there is provided a method of fabricating a semiconductor devicecomprising:

[0018] a step of forming a capacitor comprising a lower electrode formedon a semiconductor substrate, a capacitive insulator made up of a metaloxide film, formed on the lower electrode, and an upper electrode formedon the capacitive insulator;

[0019] a step of forming an interlayer insulator on top of the capacitorand the semiconductor substrate;

[0020] a step of forming a hole in the interlayer insulator for exposingthe top face of the electrodes of the capacitor;

[0021] a step of forming a metal pattern inside the hole for electricalconnection with the electrodes of the capacitor;

[0022] a step of forming an insulating film having a low waterconstituent content on top of the metal pattern inside the hole; and

[0023] a step of forming a water constituents diffusion preventive filmon top of the metal pattern or the insulating film having the low waterconstituent content.

[0024] Thus, the invention can provide the method of fabricating thesemiconductor device comprising the ferroelectric capacitor using anoble metal having a catalytic action as the constituent material of theelectrodes, wherein evolution of hydrogen atoms, caused by the catalyticaction of the constituent material of the electrodes, can be suppressed,so that the ferroelectric memory of the semiconductor device is capableof maintaining satisfactory memory characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] While the specification concludes with claims particularlypointing out and distinctly claiming the subject matter which isregarded as the invention, it is believed that the invention, theobjects, features and advantages thereof will be better understood fromthe following description taken in connection with the accompanyingdrawings in which:

[0026]FIG. 1 is a sectional view of a semiconductor device fabricatedaccording to a first embodiment of the invention;

[0027]FIG. 2 is an expanded view of a metal pattern of the semiconductordevice fabricated according to the first embodiment of the invention;

[0028]FIG. 3 is an expanded view of a first variation of the metalpattern of the semiconductor device fabricated according to the firstembodiment of the invention;

[0029]FIG. 4 is an expanded view of a second variation of the metalpattern of the semiconductor device fabricated according to the firstembodiment of the invention; and

[0030]FIG. 5 is an expanded view of a metal pattern of a semiconductordevice fabricated according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Preferred embodiments of the invention are described in detailhereinafter with reference to the accompanying drawings. First, a firstembodiment of the invention is described.

[0032]FIG. 1 is a sectional view showing a semiconductor devicefabricated according to the first embodiment of the invention, and FIGS.2 to 4 are expanded views showing a metal pattern in FIG. 1, asexpanded.

[0033] As shown in FIG. 1, a ferroelectric memory according to theinvention comprises a semiconductor substrate 1, a transistor 2comprised of a source region 2 a and a drain region 2 b, formed on asurface of the semiconductor substrate 1, and a gate electrode 2 cformed on the semiconductor substrate 1 between the source region 2 aand the drain region 2 b, and a first interlayer insulator 3, a secondinterlayer insulator 4, a third interlayer insulator 5, and apassivation film 6 that are formed in that order on top of thesemiconductor substrate switch 1.

[0034] Further, on top of the first interlayer insulator 3, there isprovided a ferroelectric capacitor 7 comprising a lower electrode 7 aand an upper electrode 7 b, made of material having a catalytic action,such as, for example, platinum (Pt), and a ferroelectric film 7 c madeup of a metal oxide film such as PZT, SBT, and so forth.

[0035] There are provided a contact hole 9 a reaching the semiconductorsubstrate 1 in the first interlayer insulator 3 and the secondinterlayer insulator 4, and a contact hole 9 b reaching the upper andlower electrodes 7 a, 7 b of the ferroelectric capacitor 7 in the secondinterlayer insulator 4, respectively. And inside the contact holes 9 a,9 b, there is formed a first metal pattern 11 a to be electricallyconnected with the transistor 2 and the ferroelectric capacitor 7,respectively.

[0036] Further, with the semiconductor device shown in FIG. 1, accordingto the first embodiment, a through hole 10 reaching the first metalpattern 11 a is provided in the third interlayer insulator 5, and insidethe through hole 10, a second metal pattern 11 b to be electricallyconnected with the first metal pattern 11 a is formed. That is, thesemiconductor device fabricated according to the present embodiment hasa multilayered structure wherein a plurality of the first metal patterns11 a and the second metal patterns 11 b are stacked.

[0037] On at least the side face of the first metal pattern 11 a, thereis formed a first protection film 12 having capability of preventingdiffusion of water constituents and high coating power, thereby coveringthe side face of the first metal pattern 11 a. With the semiconductordevice according to the present embodiment, shown in FIG. 2(a), thefirst protection film 12 is formed to a substantially identicalthickness on both the top face and the side face of the first metalpattern 11 a. For the first protection film 12, use is preferably madeof a film not containing water constituents and evolving no hydrogenduring the formation of the film, such as a metal oxide film with apassivated surface. Further, the first protection film 12 preferably isa film more insusceptible to oxidation than the constituent material ofthe first metal pattern 11 a, such as, for example, aluminum (Al),titanium (Ti) and tungsten (W).

[0038] In addition, in the case of the present embodiment, since thefirst protection film 12 is formed so as to span an interval between thefirst metal patterns 11 a adjacent to each other, the film for use asthe first protection film 12 is preferably a film having electricresistivity to such an extent that problems such as cross talk and shortcircuit between the metal patterns are not caused to occur, that is, ahighly insulating film having electric resistivity in the order of notless than 1×10¹⁰ Ωm.

[0039] Examples of the first protection film 12 include films, such as atitanium oxide (TiO) film, an aluminum oxide (Al₂O₃) film, and so forth,formed by the well-known chemical vapor deposition (CVD) method, and soforth.

[0040] In this connection, when comparing the TiO film with the Al₂O₃film as films for use as the first protection film 12, use of the Al₂O₃film having lower stabilizing energy, after bonding with oxygen, for thefirst protection film 12 will enable prevention of oxidation of thefirst metal pattern 11 a with greater certainty in comparison with thecase of using the TiO film.

[0041] Now, the first metal pattern 11 a according to the invention isdescribed in detail hereinafter by referring to FIGS. 2 to 4 which areexpanded views showing principal parts of the first metal pattern 11 aas expanded. FIG. 2 (a) is an expanded sectional view of the first metalpattern 11 a in FIG. 1, and FIG. 2(b) is an expanded cross-sectionalview taken on line X-X in FIG. 1 of the first metal pattern 11 a formedinside the contact hole 9 b in FIG. 1.

[0042] The first metal patterns 11 a to be electrically connected withthe ferroelectric capacitor 7 and the transistor 2, respectively,comprise an adhesion layer 21 made up of a TiN layer or a laminated filmof a Ti layer and a TiN layer, and a wiring layer 22 formed on top ofthe adhesion layer 21. The wiring layer 22 is made up of a layercomposed mainly of Al or a layer composed mainly of W, and the firstmetal pattern 11 a is formed by patterning after forming the adhesionlayer 21 and the wiring layer 22 in that order. That is, as shown inFIG. 2(a), the first metal pattern 11 a is constructed such that thewiring layer 22 poses a risk of the side face thereof, in particular,coming in contact with water constituents and the wiring layer 22susceptible to oxidation is exposed.

[0043] Accordingly, with the semiconductor device according to theinvention, on the top face and the side face of the first metal pattern11 a comprised of the adhesion layer 21 and the wiring layer 22, thefirst protection film 12 that has capability of preventing diffusion ofwater constituents and is formed to a substantially identical thicknesson both the top face and the side face of the first metal pattern 11 a,in other words, the first protection film 12 having a high coating poweris formed to a thickness in the order of about 50 to 200 nm.

[0044] With such a constitution as described being adopted, it becomespossible to ensure prevention of the side face of the first metalpattern 11 a from coming in contact with water constituents, which cannot be fully attained by the agency of a water constituents diffusionpreventive film 8 that is formed by a sputtering method and so forthafter the formation of the first protection film 12 since it isdifficult to form a film to a sufficient thickness on the side face ofthe first metal pattern 11 a by the sputtering method. As a result,evolution of hydrogen molecules following thermal diffusion of waterconstituents can be suppressed.

[0045] Further, in the case of using a film such as an Al₂O₃ film as thefirst protection film 12, since the first protection film 12 has highcapability of oxidation resistance besides the capability of preventingdiffusion of water constituents, it is possible to prevent with greatercertainty oxidation of the surface of the metal patterns that is causedby thermal diffusion of water constituents such as constitution waterand adsorption water, contained in the interlayer insulators, byproviding the first protection film 12 on the top face and the side faceof the first metal pattern 11 a inside the contact hole 9 b, including asurface of the first metal pattern 11 a. As a result, reduction in thenumber of hydrogen molecules as evolved due to oxidation of the metalpatterns can be realized.

[0046] Further, with the semiconductor device according to theinvention, a silicon nitride film serving as the water constituentsdiffusion preventive film 8 for preventing water constituents fromdiffusing into the surface of the first metal pattern 11 a is formed onthe first protection film 12 to a thickness in the order of about 40 to200 nm by the reactive sputtering method and so forth, not requiring ahydrogen atmosphere.

[0047] Thus, by providing the water constituents diffusion preventivefilm 8 for prevention of diffusion of water constituents on top of thefirst protection film 12 for prevention of oxidation of the surface ofthe first metal pattern 11 a, it becomes possible to prevent arrival ofwater constituents at the surface of the first metal pattern 11, so thatfurther reduction in the number of hydrogen molecules as evolved due tooxidation of the metal patterns can be achieved.

[0048] Also, with the semiconductor device according to the invention,by adopting a construction such that the water constituents diffusionpreventive film 8 is provided on the second interlayer insulator 4, itbecomes possible to effectively prevent water constituents as evolvedduring a fabrication process including a back-end step of forming thepassivation film 6, and so forth, from being diffused to theferroelectric capacitor 7 installed in the second interlayer insulator4.

[0049] The water constituents diffusion preventive film 8 is preferablyformed at least on the second interlayer insulator 4 in order tosuppress the impact of water constituents on the ferroelectric capacitor7, and in particular, is preferably formed such a way as to incorporatethe first metal pattern 11 a as patterned and the first protection film12 formed on top of the first metal pattern 11 a.

[0050] Further, by forming the water constituents diffusion preventivefilm 8 to a thickness in the order of about 40 to 160 nm, it becomespossible to protect the ferroelectric capacitor 7 from waterconstituents contained in the third interlayer insulator 5 and waterconstituents as evolved in the course of the fabrication process.

[0051] The water constituents diffusion preventive film 8 is preferablymade up of a silicon nitride film (Si_(x)N_(x) film) or an oxidizedsilicon nitride film (SiON film), formed by the reactive sputteringmethod that requires no hydrogen atmosphere, in order to lessen theimpact of hydrogen during fabrication in consideration of corrosionresistance against water constituents, and heat resistance encounteredin various methods of fabrication.

[0052] For other layers and elements, the conventional and well-knownmaterials can be employed.

[0053] For the semiconductor substrate 1, a silicon (Si) substrate canbe employed, and for the first, second, and third interlayer insulators3, 4, 5, a silicon oxide film (SiO₂ film), and so forth, formed by, forexample, the CVD method, can be employed. And for the passivation film6, a silicon nitride film, and so forth, formed by the CVD method, canbe employed.

[0054] Further, with the semiconductor device according to theinvention, a hydrogen diffusion preventive film 31 for prevention ofhydrogen diffusion may be formed on top of the water constituentsdiffusion preventive film 8 to a thickness in the order of about 50 to200 nm as shown in FIG. 3. By forming the hydrogen diffusion preventivefilm 31, the impact of hydrogen on the ferroelectric capacitor 7 can berendered less even at the time of the formation of the passivation film6 to be performed under a hydrogen atmosphere.

[0055] The hydrogen diffusion preventive film 31 need only be formed atleast underneath the passivation film 6, and is preferably formed overthe first protection film 12 or the first metal pattern 11 a. Inparticular, if the hydrogen diffusion preventive film 31 is formedimmediately before the formation of the passivation film 6, this willprevent the hydrogen diffusion preventive film 31 from being exposed toan atmosphere of hydrogen evolved when forming the interlayer insulatorsand so forth by use of a plasma, thereby enabling a high hydrogenbarrier characteristic to be maintained. For the hydrogen diffusionpreventive film 31 according the present embodiment, use of tantalumoxide (Ta₂O₅), aluminum oxide (Al₂O₃), and so forth is preferable, andparticularly from the viewpoint of workability, use of tantalum oxidefor the hydrogen diffusion preventive film 31 is preferable.

[0056] Further, as shown in FIG. 4, the semiconductor device accordingto the present embodiment may be constructed such that after depositingthe first protection film 12 on the top and side faces of the firstmetal pattern 11 a, a portion of the first protection film 12, on thetop face of the first metal pattern 11 a, is removed by etching tothereby form a sidewall 12 a made up of the first protection film 12 onthe side face of the first metal pattern 11 a, and a water constituentsdiffusion preventive film 8 for prevention of diffusion of waterconstituents is formed on the sidewall 12 a and the first metal pattern11 a. With such a constitution described as above, however, the wiringlayer 22 susceptible to oxidation will be exposed on the top face of thefirst metal pattern 11 a, and accordingly, the first metal pattern 11 apreferably has a multilayered construction comprising the wiring layer22 and a protective layer 23 for preventing oxidation of the wiringlayer 22, formed on top of the wiring layer 22.

[0057] A layer serving as the protective layer 23 of the first metalpattern 11 a is selected in consideration of adhesiveness, and so forth,with the wiring layer 22, and a layer made up of a TiN layer, or alaminated layer of a Ti layer and a TiN layer, and so forth ispreferably used as the protective layer 23.

[0058] With the semiconductor device comprising the sidewall 12 a of thefirst protection film 12, it becomes possible to prevent with certaintyshort circuit which is likely to occur between the adjacent first metalpatterns 11 a owing to the first protection film 12 formed so as to spanacross a plurality of the first metal patterns 11 a in the case of, forexample, insufficient introduction of oxygen or insufficient reaction ofconstituent metals with oxygen in the step of forming the firstprotection film 12 such the TiO film or the Al₂O₃ film formed by thereactive sputtering method as in the case of the semiconductor deviceshown in FIG. 2.

[0059] It also becomes possible to prevent with certainty short circuitwhich is likely to occur in the case where there occur progress inreduction of the first protection film 12 and a drop in electricresistance thereof in the later steps of a process of fabricating thesemiconductor device.

[0060] Further, if the first protection film 12 is rendered into theshape of the sidewall 12 a around the first metal pattern 11 a, thiswill enable an angle of the bent corners of the first metal pattern 11 ato be moderated, so that a coating ratio of a film formed after thefirst protection film 12 can be improved.

[0061] In particular, as for the water constituents diffusion preventivefilm 8 formed on the first protection film 12, since a silicon nitridefilm formed by the reactive sputtering method that is hard to bedeposited on the sidewall is used as the water constituents diffusionpreventive film 8, an angle formed between the top face and side face ofthe first metal pattern 11 a is moderated by the tapered face of thefirst protection film provided on the side face of the first metalpattern 11 a, thereby enabling the coating ratio to be further improved.In addition, it becomes possible to secure a sufficient thickness of thewater constituents diffusion preventive film 8 also on the side face ofthe first metal pattern 11 a, thereby enhancing capability of preventingwater constituents from coming into contact with the first metal pattern11 a.

[0062] On the assumption that, for example, a thickness of the firstmetal pattern 11 a is in the order of about 300 to 500 nm, and athickness of the sidewall 12 a is in the order of about 200 nm, an angleθ formed between the tapered face of the sidewall 12 a of the firstprotection film 12, formed on the side face of the first metal pattern11 a, and the top face of the first metal pattern 11 a will be about70°, thereby enabling the coating ratio of the water constituentsdiffusion preventive film 8 to be improved by a factor of not less thanabout 1.6 in comparison with the same in the case where an angle 0between the first protection film 12, not formed in the shape of thesidewall 12 a, and the top face of the first metal pattern 11 a is about90°.

[0063] Further, with the semiconductor device comprising the firstprotection film 12 in the shape of the sidewall 12 a, a hydrogendiffusion preventive film 31 may be formed on the water constituentsdiffusion preventive film 8 as shown in FIG. 3.

[0064] A method of fabricating the semiconductor device according to thefirst embodiment of the invention, shown in FIG. 1, is describedhereinafter.

[0065] First, the transistor 2 comprising the source region 2 a, drainregion 2 b, and gate electrode 2 c is formed on a Si substrate as thesemiconductor substrate 1 by the well-known method.

[0066] Thereafter, the first interlayer insulator 3 made up of a siliconoxide film is formed on the semiconductor substrate 1 incorporating thetransistor 2 by the well-known CVD method and so forth.

[0067] Subsequently, the ferroelectric capacitor 7 comprising the lowerelectrode 7 a, the upper electrode 7 b, made of noble metal, such as Ptand so forth, and the ferroelectric film 7 c made up of a metal oxidefilm is formed on the first interlayer insulator 3 before forming thesecond interlayer insulator 4 on top of the first interlayer insulator 3with the ferroelectric capacitor 7 formed thereon.

[0068] After the formation of the second interlayer insulator 4, heattreatment at a temperature in a range of 700 to 800° C. is appliedthereto for 1 to 2 hours to thereby remove water constituents (OHcompounds) such as constitution water contained in the first, and secondinterlayer insulators 3, 4. There is no particular limitation to anatmosphere under which the heat treatment described above is to beapplied unless it is a reducing atmosphere, however, from the viewpointof making up, for oxygen deficiency in the ferroelectric film 7 c, theheat treatment is preferably applied under an oxygen atmosphere.

[0069] Subsequently, a resist mask having openings is formed on thesecond interlayer insulator 4, and the contact hole 9 a reaching thetransistor 2 is formed in the first interlayer insulator 3, and thesecond interlayer insulator 4, and the contact hole 9 b reaching theelectrodes of the ferroelectric capacitor 7 is formed in the secondinterlayer insulator 4, respectively. Then, the first metal pattern 11 afor electrical connection with the transistor 2, and the ferroelectriccapacitor 7 is formed inside the contact holes 9 a, 9 b, respectively.In forming the first metal pattern 11 a, a TiN film to serve as theadhesion layer 21 is first formed to a thickness in the order of about100 nm. Subsequently, for example, an Al film to serve as the wiringlayer 22 is sequentially formed to a thickness in the order of about 300nm by the sputtering method and is then etched into a pattern asdesired. As a result, the first metal patterns 11 a are formed.

[0070] In this case, the protective layer 23 made up of a TiN film or alaminated film composed of Ti and TiN for protecting the top face of thewiring layer 22 from oxidation may be formed on top of the wiring layer22 prior to a step of patterning.

[0071] After the formation of the first metal pattern 11 a, the firstprotection film 12 for preventing diffusion of water constituents isformed on the top face and side face of the respective first metalpatterns 11 a by a film-forming method having excellent coatingperformance such as a CVD method, and so forth. For the first protectionfilm 12 according to the present embodiment, use is made of an Al₂O₃film and so forth, formed by the well-known CVD method. As the firstprotection film 12, use is preferably made of a film that does not causeevolution of hydrogen when the film is formed, does not contain waterconstituents therein, and can be formed with an excellent coating power.Further, the first protection film 12 is preferably a film not onlyhaving capability of preventing diffusion of water constituents but alsomore insusceptible to oxidation than the constituent material of thefirst metal pattern 11 a, and highly insulating. The film need only beformed to a thickness in the order of about 50 to 200 nm.

[0072] Thereafter, a Si₃N₄ film serving as the water constituentsdiffusion preventive film 8 is formed to a thickness in the order ofabout 100 nm by use of a reactive sputtering system (manufactured byShinko Seiki Co., Ltd.).

[0073] With the present invention, in forming the water constituentsdiffusion preventive film 8 that is effective in prevention of theimpact of water constituents, the reactive sputtering method is adopted,so that the water constituents diffusion preventive film 8 can be formedin a condition where an amount of hydrogen and nitrogen that have strongeffects on deterioration of the characteristic of the ferroelectriccapacitor will be remarkably decreased as compared with the case offorming the film by the CVD method.

[0074] Now, the reactive sputtering method is a technique for forming athin film made of a metal compound on a substrate by introducing a raregas into a film-forming enclosure (sputter chamber) where the substrateand a sputter target are disposed, causing plasma discharge to occur byapplying a negative high voltage to a sputter electrode (cathode) withthe target attached thereto, thereby sputtering the target by the agencyof a rare gas plasma, and simultaneously introducing an active gas, forexample, a nitrogen (N₂) gas so as to cause reaction between the activegas and the constituent material of the target.

[0075] As for the conditions under which the reactive sputtering methodis applied, it is preferably applied under an atmosphere of a mixed gasof a nitrogen gas, and so forth, as the active gas, and an argon gas,and so forth, as the rare gas, mixed approximately at a ratio of 1:1,and at a pressure in a range of 0.04 to 0.15 Pa, with an RF power sourcebeing in the order of 1 to 3 kW.

[0076] Accordingly, with the method according to the invention, asputtering condition for the formation of the water constituentsdiffusion preventive film 8 is adopted such that a Si target is used, anAr gas and a N₂ gas are introduced at a low rate of 1:1, and at apressure of 1330 Mpa (10 mTorr) with an RF power source at 2.5 kW.

[0077] After the formation of the water constituents diffusionpreventive film 8, a SiO₂ film as the third interlayer insulator 5 isfurther formed on top of the water constituents diffusion preventivefilm 8 to a thickness in the order of about 400 nm by the well-known CVDmethod. Thereafter, a resist mask having openings are formed on top ofthe third interlayer insulator 5, and a through-hole 10 reaching thefirst metal pattern 11 a is formed in the third interlayer insulator 5by use of the resist mask. Inside the through-hole 10 thus formed, thereis formed a second metal pattern 11 b for electrically connectingperipheral circuits with a ferroelectric memory cell comprised of thetransistor 2 and the ferroelectric capacitor 7. The second metal pattern11 b is formed of Al (thickness: 700 nm) and TiN (thickness: 100 nm) bythe sputtering method, and subsequently, is patterned into a pattern asdesired.

[0078] Finally, a Si₃N₄ film to serve as the passivation film 6 isformed to a thickness about 850 nm by the CVD method, therebyfabricating the semiconductor device according to the invention,comprising the ferroelectric memory.

[0079] In the case where the first metal pattern 11 a is provided withthe protective layer 23, after the formation of the first protectionfilm 12 on the top and side faces of the first metal pattern 11 a, astep of etching back the entire surface of the first protection film 12,and forming the sidewall 12 a of the first protection film 12 on theside face of the first metal pattern 11 a may be added before formingthe water constituents diffusion preventive film 8 of the Si₃N₄ filmwhich is be formed by the reactive sputtering method.

[0080] By forming the sidewall 12 a in the step described, the angle ofthe bent corners of the first metal pattern 11 a can be moderated,thereby enabling the coating ratio of the water constituents diffusionpreventive film 8, and so forth, covering the first metal pattern 11 a,to be enhanced.

[0081] Further, with the method of fabricating the semiconductor deviceaccording to the present embodiment, after the formation of the firstmetal pattern 11 a for electrically interconnecting the transistor 2 andthe ferroelectric capacitor 7, a hydrogen diffusion preventive film 41made up of a Ta₂O₅ film, and so forth, effective in prevention of theimpact of hydrogen, may be similarly formed on the first metal pattern11 a to a thickness in the order of about 170 nm by the reactivesputtering method. As for sputtering conditions for forming the hydrogendiffusion preventive film 41, the conditions are adopted such that thefilm is formed by using a Ta target, and introducing an Ar gas and an O₂gas into a sputtering chamber at a flow ratio of 1:1 at a pressure of1330 mPa (10 mTorr), with an RF power source at 2.5 kW.

[0082] As with the present embodiment described above, by providing thefirst protection film 12 on the first metal pattern 11 a, and providingfurther the water constituents diffusion preventive film 8 formed by thereactive sputtering method, and so forth, on top of the first protectionfilm 12, it becomes possible to prevent thermal diffusion of waterconstituents into the first metal pattern 11 a from the films containingan abundance of constitution water, such as the third interlayerinsulator 5 made of a silicon oxide film, silicon nitride film, and soforth, or the passivation film, which are formed in the steps after theformation of the first metal pattern 11 a during the process offabricating the semiconductor device. Furthermore, even if there occursthermal diffusion of water constituents into the first metal pattern 11a, oxidation of the constituent material of the first metal pattern 11a, such as Al, W, and Ti, by the agency of water constituents can besuppressed because the wiring layer 22 of the first metal pattern 11 a,very susceptible to oxidation, is covered by the first protection film12 whose energy for bonding with oxygen is sufficiently low. As aresult, it becomes possible to reduce evolution of hydrogen molecules,accompanying oxidation of the first and second metal patterns 11 a, 11b.

[0083] That is, it becomes possible to provide the method of fabricatingthe semiconductor device capable of maintaining satisfactoryferroelectricity and ferroelectric capacitor characteristics as aferroelectric memory.

[0084] Further, as a result of adoption of the construction in which thefirst protection film 12 in the shape of a sidewall is provided on theside face of the first metal patterns 11 a, the angle of the bentcorners of the first metal patterns 11 a can be moderated. Accordingly,evolution of hydrogen and nitrogen, adversely affecting theferroelectric capacitor, can be suppressed, and, in addition, even inthe case of using the reactive sputtering method by which a film can beformed at a low temperature, the water constituents diffusion preventivefilm 8 with a sufficiently large thickness secured can be formed on theside face of the first metal patterns 11 a, respectively.

[0085] Thus, according to the present embodiment of the invention, it ispossible to further enhance capability for preventing water constituentsfrom contacting the first metal patterns 11 a, so that a semiconductordevice capable of maintaining more satisfactory ferroelectricity andferroelectric capacitor characteristics as a ferroelectric memory can befabricated.

[0086] Next, a second embodiment of a method of fabricating asemiconductor device according to the invention is describedhereinafter.

[0087] FIGS. 5(a) and 5(b) are views showing the method of fabricatingthe semiconductor device according to the second embodiment, FIG. 5(a)is an expanded sectional view of the first metal pattern 11 a in FIG. 1,and FIG. 5 (b) is an expanded cross-sectional view taken on line X-X inFIG. 1 of the first metal pattern 11 a formed inside the contact hole 9b in FIG. 1. In these figures, parts identical to, or corresponding tothose shown in the first embodiment are denoted by like referencenumerals.

[0088] The method of fabricating the semiconductor device according tothe second embodiment differs from that according to the firstembodiment in that a water constituents diffusion preventive film 8 tobe formed on the first metal pattern 11 a is provided through theintermediary of a silicon oxide film 51 that is not prone to evolutionof hydrogen at the time of film formation and has low water constituentcontent, composed mainly of material such as, for example, tetraethylorthosilicate (TEOS).

[0089] The construction of the semiconductor device according to thesecond embodiment is described hereinafter.

[0090] As shown in FIG. 5, as with the previously describedsemiconductor device according to the first embodiment, thesemiconductor device according to the second embodiment is constructedsuch that the first metal pattern 11 a comprising an adhesion layer 21made up of a TiN layer or a laminated film of a Ti layer and a TiNlayer, and a wiring layer 22 formed on top of the adhesion layer 21 canbe electrically connected with a ferroelectric capacitor 7 and atransistor 2.

[0091] Subsequently, on the top and side faces of the first metalpattern 11 a, a TiO film, an Al₂O₃ film, and so forth, serving as afirst protection film 12, is formed to a thickness in the order of about50 to 200 nm.

[0092] With the semiconductor device according to the second embodiment,after the formation of the first protection film 12, the silicon oxidefilm 51 that is not prone to evolution of hydrogen at the time of filmformation and has low water constituent content, composed mainly ofmaterial such as, for example, tetraethyl orthosilicate (TEOS), isformed on top of the first protection film 12 and the first metalpattern 11 a. Further, in the case of using a metal having a highmelting point such as TiN, and so forth, as the constituent material ofthe first metal pattern 11 a, it is possible to form a film having stilllower water constituent content by using a silicon oxide film composedmainly of TEOS, formed particularly under a reduced pressure, forexample, at, for example, not higher than about 0.3 Torr.

[0093] Now, the water constituents referred to herein includes surfaceadsorption water (H₂O), constitution water (Si—OH and Si—OH combinedwith a OH group through hydrogen bond that severs bond with Si whenheated, producing H₂O), and so forth. Thus, a contact hole 9 b is filledup with the first metal pattern 11 a that is formed inside the contacthole 9 b and the insulating film 51 whose water constituent content islow. Accordingly, a thickness of the silicon oxide film 51 formed on thefirst metal pattern 11 a is preferably not less than about half theinside diameter of the contact hole 9 b so as to enable the interior ofthe contact hole 9 b to be filled up with the silicon oxide film 51.

[0094] Then, after the formation of the silicon oxide film 51, a waterconstituents diffusion preventive film 8 is formed on the silicon oxidefilm 51 by the sputtering method and so forth.

[0095] With the present embodiment, by forming the film, not prone toevolution of hydrogen at the time of film formation, and having lowwater constituent content, inside the hole beforehand, it becomespossible to form the water constituents diffusion preventive film 8capable of enhancing a coating ratio and sufficiently preventingdiffusion of water constituents even along the sidewall of the contacthole 9 b where it is difficult to secure a sufficient thickness of thewater constituents diffusion preventive film 8 to be formed by thesputtering method.

[0096] Needless to say, as with the previously described semiconductordevice according to the first embodiment, after the formation of thewater constituents diffusion preventive film 8, a hydrogen diffusionpreventive film 41 made up of a Ta₂O₅ film, and so forth, for preventionof diffusion of hydrogen into a ferroelectric capacitor, may besimilarly formed on the water constituents diffusion preventive film 8to a thickness in the order of about 170 nm by the reactive sputteringmethod.

[0097] Thus, by providing the water constituents diffusion preventivefilm 8 through the intermediary of the silicon oxide film 51, the waterconstituents diffusion preventive film 8 having a sufficiently largethickness can be deposited, and in particular, it becomes possible toprevent deterioration in the capability of the water constituentsdiffusion preventive film 8 for preventing diffusion of waterconstituents inside the contact hole 9 b, caused by a portion of thewater constituents diffusion preventive film 8, having a smallerthickness, along the sidewall of the contact hole 9 b.

[0098] As described hereinbefore, with the method of fabricating thesemiconductor device according to the invention wherein the surface ofthe metal patterns susceptible to oxidation is coated with the firstprotection film, and the water constituents diffusion preventive film isformed on the first protection film by the reactive sputtering method,and so forth, it becomes possible to reduce evolution of hydrogenmolecules, accompanying oxidation of the surface of the metal patterns,which is caused by the water constituents contained in the interlayerinsulators and so forth, and also to suppress evolution of hydrogenatoms, caused by the catalytic action of the electrodes made of a noblemetal such as platinum, and so forth. That is, it is possible to protectthe ferroelectric capacitor from the water constituents that are evolvedduring the fabrication process, thereby providing the ferroelectriccapacitor maintaining satisfactory memory characteristics. Also, sincethe water constituents diffusion preventive film having a sufficientlylarge thickness can be provided, it becomes possible to provide aferroelectric memory capable of reducing the impact of hydrogen evolvedwhen forming the passivation film, and so forth that are to be formed ina hydrogen atmosphere.

[0099] Further, with the semiconductor device fabricated according tothe present embodiment as well, a constitution may be adopted such thata sidewall 12 a of the first protection film 12 is provided as with thecase of the first embodiment. In such a case, it becomes possible toprevent with certainty short circuit which is likely to occur betweenthe adjacent first metal patterns 11 a owing to the first protectionfilm 12 formed so as to span across a plurality of the first metalpatterns 11 a, in the case of, for example, insufficient introduction ofoxygen or insufficient reaction of constituent metals with oxygenoccurring in the step of forming the first protection film 12 such a TiOfilm and Al₂O₃ film by the reactive sputtering method.

[0100] Further, it also becomes possible to prevent with certainty shortcircuit which is likely to occur in the case where there occur progressin reduction of the first protection film 12 and a drop in electricresistance thereof in the later steps of the process of fabricating thesemiconductor device.

[0101] Further, if the first protection film 12 is formed in the shapeof the sidewall 12 a around the first metal pattern 11 a, an angle ofthe bent corners of the first metal pattern 11 a can be moderated, sothat a coating ratio of films formed after the first protection film 12can be improved, and since a sufficiently large thickness of the waterconstituents diffusion preventive film 8 can be secured even along theside face of the first metal pattern 11 a, the capability thereof forpreventing water constituents from coming in contact with the firstmetal pattern 11 a can be enhanced.

What is claimed is:
 1. A method of fabricating a semiconductor devicecomprising: forming a capacitor comprising a lower electrode formed on asemiconductor substrate, a capacitive insulator made up of a metal oxidefilm, formed on the lower electrode, and an upper electrode formed onthe capacitive insulator; forming a metal pattern to be electricallyconnected to the electrodes of the capacitor; forming a first protectionfilm which coats at least a side face of the metal pattern; and forminga water constituents diffusion preventive film on the side face and topface of the metal pattern through the intermediary of the firstprotection film.
 2. A method of fabricating a semiconductor deviceaccording to claim 1, wherein the first protection film preventsdiffusion of water constituents, and oxidation of the metal pattern. 3.A method of fabricating a semiconductor device according to claim 1,wherein the first protection film is made up of a highly insulating andpassivated metal oxide film.
 4. A method of fabricating a semiconductordevice according to claim 1, wherein the first protection film is formedby use of the chemical vapor deposition method.
 5. A method offabricating a semiconductor device according to claim 1, furthercomprising etching the first protection film, and forming a sidewall ofthe first protection film on the side face of the metal pattern, therebyforming the water constituents diffusion preventive film on the sidewalland the metal pattern.
 6. A method of fabricating a semiconductor deviceaccording to claim 5, wherein the metal pattern comprises a conductivelayer to be electrically connected to the capacitor and a protectivelayer which protects the top face of the conductive layer, and theprotective layer is exposed out of the first protection film by etchingthe first protection film.
 7. A method of fabricating a semiconductordevice according to claim 5, wherein, in etching the first protectionfilm, a tapered face is formed on the side face of the first protectionfilm, and an angle formed between the tapered face and the top face ofthe conductive layer is not greater than about 70°.
 8. A method offabricating a semiconductor device according to claim 1, wherein thewater constituents diffusion preventive film is formed by a reactivesputtering method.
 9. A method of fabricating a semiconductor deviceaccording to claim 8, wherein the reactive sputtering method is executedin a mixed gas atmosphere containing nitrogen and a rare gas, ornitrogen, oxygen and a rare gas.
 10. A method of fabricating asemiconductor device according to claim 1, further comprising forming ahydrogen diffusion preventive film on top of the metal pattern.
 11. Amethod of fabricating a semiconductor device comprising: forming acapacitor comprising a lower electrode formed on a semiconductorsubstrate, a capacitive insulator made up of a metal oxide film, formedon the lower electrode, and an upper electrode formed on the capacitiveinsulator; forming an interlayer insulator on top of the capacitor andthe semiconductor substrate; forming a hole in the interlayer insulatorfor exposing a top face of the electrodes of the capacitor; forming ametal pattern inside the hole for electrical connection with theelectrodes of the capacitor; forming an insulating film having a lowwater constituent content on the metal pattern inside the hole; andforming a water constituents diffusion preventive film on the metalpattern or the insulating film having the low water constituent content.12. A method of fabricating a semiconductor device according to claim11, wherein the sum of a thickness of the metal pattern inside the holeand a thickness of the insulation film having the low content of waterconstituents, inside the hole, as measured from the bottom face of thehole, is substantially equivalent to not less than a thickness of theinterlayer insulator.
 13. A method of fabricating a semiconductor deviceaccording to claim 11, wherein, in forming the insulation film havingthe low water constituent content, a chemical vapor deposition methodusing a gas containing an organic silicon compound is employed.
 14. Amethod of fabricating a semiconductor device according to claim 11,wherein the insulation film having the low water constituent content hasa thickness substantially equivalent to not less than half of the insidediameter of the hole.
 15. A method of fabricating a semiconductor deviceaccording to claim 11, further comprising forming a first protectionfilm on the metal pattern provided inside the hole, thereby forming theinsulation film having the low water constituent content on the firstprotection film.
 16. A method of fabricating a semiconductor deviceaccording to claim 15, further comprising etching the first protectionfilm, and forming a sidewall of the first protection film on the sideface of the metal pattern, thereby forming the water constituentsdiffusion preventive film on the sidewall and the metal pattern.
 17. Amethod of fabricating a semiconductor device according to claim 16,wherein the metal pattern comprises a conductive layer for electricalconnection with the capacitor, and a protective layer for protecting atop face of the conductive layer, and the protective layer is exposedout of the first protection film by etching the first protective film.18. A method of fabricating a semiconductor device according to claim17, wherein, in etching the first protection film, a tapered face isformed on the side face of the first protection film, and an angleformed between the tapered face and the top face of the conductive layeris not greater than about 70°.
 19. A method of fabricating asemiconductor device according to claim 11, wherein the waterconstituents diffusion preventive film is formed a reactive sputteringmethod.
 20. A method of fabricating a semiconductor device according toclaim 19, wherein the reactive sputtering method is executed in a mixedgas atmosphere containing nitrogen and a rare gas, or nitrogen, oxygenand a rare gas.
 21. A method of fabricating a semiconductor deviceaccording to claim 11, further comprising forming a hydrogen diffusionpreventive film on the metal pattern.